The present invention relates to a method for installing pistons in a piston type compressor that compresses refrigerant gas in a vehicle air conditioner. Particularly, the present invention pertains to a method for installing pistons in cylinder bores and a positioning jig used for the method.
FIG. 8 illustrates a compressor. The compressor has a front housing member 101 and a cylinder block 102. The front housing member 101 is secured to the front face of the cylinder block 102 to define a crank chamber 103. A drive shaft 104 extends through the crank chamber 103 and is supported by the front housing member 101 and the cylinder block 102. A swash plate 105 is coupled to the drive shaft 104 to rotate integrally with the drive shaft 104.
Cylinder bores 106 are formed in the cylinder block 102. Each cylinder bore 106 receives a single headed piston 107. Each piston 107 is coupled to the swash plate 105 by shoes 108. The compressor performs a compression cycle. In the compression cycle, rotation of the drive shaft 104 is converted to reciprocation of the pistons 107 by the swash plate 105 and the shoes 108. Accordingly, refrigerant gas is drawn in to each cylinder bore 106 and is compressed in the cylinder bore 106. Compressed refrigerant gas is then discharged from the cylinder bore 106.
FIG. 9 illustrates a step in the assembly process of the compressor. Specifically, FIG. 9 shows a step for installing the pistons 107 into the cylinder bores 106. The pistons 107 are first coupled to the swash plate 105 to form a piston assembly Pa. A positioning jig 111 holds the pistons 107 at its circumferential position to align the axis L2 of each piston 107 with the axis N2 of the corresponding cylinder bore 106.
In this state, the piston assembly Pa and the cylinder block 102 are brought closer to each other along the axes L1 (or N1) of the piston assembly Pa and the cylinder block 102 such that each piston 107 is inserted into the corresponding cylinder bore 106 to a predetermined position. When the pistons 107 starts entering the cylinder bores 106, the jig 111 is disengaged from the pistons 107. This is because the jig 111 is no longer necessary and will hinder the further insertion of the pistons 107.
The jig 111 is formed by separable members that are moved in the radial direction to release the pistons 107. The jig 111 may be an integrated member that is moved in the direction of the axis L1 to release the pistons 107.
As illustrated by dotted lines in FIG. 9, a wall 109, which defines the crank chamber 103, extends from the cylinder block 102 in some compressors. In such a compressor, the pistons 107 cannot be installed by using the jig 111. That is, the jig 111 interferes with the wall 109 before the pistons 107 reach the cylinder bores 106. The piston assembly Pa therefore cannot be moved closer to the cylinder block 102. Thus, it is difficult to automate the installation of the pistons 107 in a compressor if the wall 109 extends by a significant axial distance from the cylinder block 102. In this case, the pistons 107 must be manually installed, which increases the costs.
If the diameter of the wall 109 is increased such that the jig 111 does not interfere with the wall 109, the pistons 107 can be installed by the jig 111. In other words, the assembly of the pistons 107 can be automated. However, the increased diameter of the wall 109 increases the size of the compressor. Since the compressor is located in a vehicle engine compartment, in which a number of other auxiliary components are located, the size of the compressor must be as small as possible.
Accordingly, it is an objective of the present invention to provide a method and a positioning jig that facilitate automation of installation of pistons in cylinder bores.
To achieve the above objective, the present invention provides a method for installing a piston in a cylinder bore formed in a cylinder block of a fluid machine. The method includes arranging the piston on one end of the cylinder block and a positioning jig on the other end of the cylinder block, inserting the positioning jig into the cylinder bore such that part of the positioning jig protrudes from the cylinder bore toward the piston, engaging the protruding part of the positioning jig with the piston to determine the position of the piston, inserting the piston into the cylinder bore while maintaining the engagement between the jig and the piston, and removing the positioning jig from the cylinder block.
The present invention further provides a positioning jig used for installing a piston in a cylinder bore formed in a cylinder block. The jig comprises a positioning member. The positioning member is inserted into the cylinder bore and protrudes from the cylinder bore. The positioning member determines the position of the piston. A positioning projection is located substantially on the axis of the positioning member. When a distal end surface of the positioning member is pressed against a corresponding end surface of the piston, the positioning projection is inserted into a recess formed substantially on the axis of the piston to align the axis of the piston with the axis of the cylinder bore.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.